System and method for positioning teeth

ABSTRACT

Methods and apparatus fit a set of upper and lower teeth in a masticatory system by generating a computer representation of the masticatory system and computing an occlusion based on interactions in the computer representation of the masticatory system.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/981,680, filed Oct. 31, 2007, which is a continuation of U.S.application Ser. No. 10/788,510, filed Feb. 27, 2004, which is acontinuation of U.S. application Ser. No. 10/133,155, filed Apr. 26,2002 (now U.S. Pat. No. 6,786,721), which is a continuation of U.S.application Ser. No. 09/169,036, filed Oct. 8, 1998 (now U.S. Pat. No.6,450,807), the full disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention is related generally to the field of orthodontics,and more particularly to a system and a method for graduallyrepositioning teeth.

A fundamental objective in orthodontics is to realign a patient's teethto positions where the teeth function optimally and aesthetically.Typically, appliances such as braces are applied to the teeth of thepatient by a treating orthodontist. Each appliance exerts continualforces on the teeth which gradually urge the teeth toward their idealpositions. Over a period of time, the orthodontist adjusts theappliances to move the teeth toward their final destination.

The process of attaching the braces to teeth is tedious and painful.Additionally, each visit to the orthodontist is time consuming andexpensive. The process is further complicated by uncertainties indetermining a final arrangement for each tooth. Generally, the finaltooth arrangement is determined by the treating orthodontist who writesa prescription. Traditionally, the prescription is based on theorthodontist's knowledge and expertise in selecting the intended finalposition of each tooth and without a precise calculation of forces beingexerted on the teeth when they contact each other.

BRIEF SUMMARY OF THE INVENTION

The invention provides a method for fitting a set of upper and lowerteeth in a masticatory system of a patient. The method generates acomputer representation of the masticatory system of the patient; anddetermines an occlusion from the computer representation of themasticatory system.

Implementations of the invention include one or more of the following.The occlusion may be a static occlusion, which is determined by modelingan ideal set of teeth; automatically applying the ideal set of teeth tothe computer representation of the masticatory system of the patient;and optimizing the position of the patient's teeth to fit the ideal setof teeth. The modeling step may select one or more arch forms specifyingthe ideal set of teeth. The applying step may include registering amodel of the upper and lower teeth with a model of the masticatorysystem; simulating the motion of the jaws to generate contact databetween the upper and lower teeth; and placing the tooth in a finalposition based on the contact data. The model may be registered usingX-ray data, computed tomography data, or data associated with amechanical model. The simulating step may apply kinematics to the modelof the teeth or a constrained motion to the model of the tooth. Theplacing step may be based on a measure of undesirability to thecontacts. The position of the tooth may be determined according to themeasure of undesirability, such as by minimizing the measure ofundesirability. The measure of undesirability may be a function of oneor more of Peer Assessment Rating (PAR) metrics, distance-based metricsand shape-based metrics. The simulating step may provide a library ofmotions with protrusive motions, lateral motions, or tooth-guidedmotions. Physical forces may be applied to the patient's jaws. Thecomputer representation of the masticatory system may be updated withnew patient data. The new patient data may be used with the old data inapplying a final position transform to the second teeth model. Thematching step may compare correspondences between the first and secondteeth models. The correspondences include feature correspondences. Thefinal position transform may include information from a newprescription.

Other implementations include one or more of the following. Theocclusion determining step includes determining one or more indicesbased on the tooth position; determining an optimality index from theindices; and setting the tooth according to the optimality index. Theoptimality determining step includes minimizing the optimality index.The indices may be based on a Peer Assessment Rating (PAR) index, adistance metric, or a shape metric. The shape metric may be derived froman arch. The indices may be based on an occlusional index or anorthodontic index. The setting of the teeth may be based on acorrespondence of tooth features, including a correspondence of toothcusps, tooth fossae, or tooth ridges. The optimality index may beoptimized using one of simulated annealing technique, hill climbingtechnique, best-first technique and heuristics technique. Theimplementation may determine whether a tooth movement reduces the index.The tooth movement may be made along each major axis and may includerotations. The tooth position may be updated if the tooth movementreduces the index.

In a second aspect, a computer-implemented apparatus defines a fitbetween a set of upper and lower teeth in a masticatory system of apatient. The apparatus comprises instructions operable to cause aprogrammable processor to generate a computer representation of themasticatory system of the patient; and determining an occlusion from thecomputer representation of the masticatory system.

Implementations of this aspect include one or more of the following. Theinvention may determine a static occlusion through instructions to modelan ideal set of teeth; automatically apply the ideal set of teeth to thecomputer representation of the masticatory system of the patient; andoptimize the position of the patient's teeth to fit the ideal set ofteeth. The occlusion determining instruction may also includeinstructions to: determine one or more indices based on the toothposition; determine an optimality index from the indices; and set thetooth according to the optimality index.

In another aspect, a system for defining a fit between a set of upperand lower teeth in a masticatory system of a patient includes aprocessor; a display device coupled to the processor; and a data storagedevice coupled to the processor, the data storage device storinginstructions operable to cause the processor to generate a computerrepresentation of the masticatory system of the patient and determine anocclusion from the computer representation of the masticatory system.

In another aspect, a system for generating one or more appliances for apatient includes a processor; a display device coupled to the processor;a data storage device coupled to the processor; a scanner coupled to theprocessor for providing data to model the masticatory system; means fordefining a fit between a set of upper and lower teeth in a masticatorysystem of the patient; and a dental appliance fabrication machinecoupled to the processor for generating the appliances in accordancewith the fit of the teeth.

Advantages of the invention include one or more of the following. When aprescription or other final designation is provided, a computer modelcan be generated and manipulated to match the prescription. Theprescription may be automatically interpreted in order to generate animage as well as a digital data set representing the final tootharrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational diagram showing the anatomical relationship ofthe jaws of a patient.

FIG. 2A illustrates in more detail the patient's lower jaw and providesa general indication of how teeth may be moved by the methods andapparatus of the present invention.

FIG. 2B illustrates a single tooth from FIG. 2A and defines how toothmovement distances are determined.

FIG. 2C illustrates the jaw of FIG. 2A together with an incrementalposition adjustment appliance which has been configured according to themethods and apparatus of the present invention.

FIG. 3 is a block diagram illustrating a process for producingincremental position adjustment appliances.

FIG. 4 is a flow chart illustrating a process for optimizing a finalplacement of the patient's teeth.

FIG. 5 is a flow chart illustrating a process for performing functionalocclusion on the patient's teeth.

FIG. 6 is a flow chart illustrating an optional process forincorporating midtreatment information to the final placement of thepatient's teeth.

FIG. 7 is a block diagram illustrating a system for generatingappliances in accordance with the present invention.

FIG. 8 shows an exemplary process for fitting the ideal teeth.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a skull 10 with an upper jaw bone 22 and a lower jaw bone20. The lower jaw bone 20 hinges at a joint 30 to the skull 10. Thejoint 30 is called a temporomandibular joint (TMJ). The upper jaw bone22 is associated with an upper jaw 101, while the lower jaw bone 20 isassociated with a lower jaw 100.

A computer model of the jaws 100 and 101 is generated, and a computersimulation models interactions among the teeth on the jaws 100 and 101.The computer simulation allows the system to focus on motions involvingcontacts between teeth mounted on the jaws. The computer simulationallows the system to render realistic jaw movements which are physicallycorrect when the jaws 100 and 101 contact each other. The model of thejaw places the individual teeth in a treated position. Further, themodel can be used to simulate jaw movements including protrusivemotions, lateral motions, and “tooth guided” motions where the path ofthe lower jaw 100 is guided by teeth contacts rather than by anatomicallimits of the jaws 100 and 101. Motions are applied to one jaw, but mayalso be applied to both jaws. Based on the occlusion determination, thefinal position of the teeth can be ascertained.

Referring now to FIG. 2A, the lower jaw 100 includes a plurality ofteeth 102, for example. At least some of these teeth may be moved froman initial tooth arrangement to a final tooth arrangement. As a frame ofreference describing how a tooth may be moved, an arbitrary centerline(CL) may be drawn through the tooth 102. With reference to thiscenterline (CL), each tooth may be moved in orthogonal directionsrepresented by axes 104, 106, and 108 (where 104 is the centerline). Thecenterline may be rotated about the axis 108 (root angulation) and theaxis 104 (torque) as indicated by arrows 110 and 112, respectively.Additionally, the tooth may be rotated about the centerline. Thus, allpossible free-form motions of the tooth can be performed.

FIG. 2B shows how the magnitude of any tooth movement may be defined interms of a maximum linear translation of any point P on a tooth 102.Each point P1 will undergo a cumulative translation as that tooth ismoved in any of the orthogonal or rotational directions defined in FIG.2A. That is, while the point will usually follow a nonlinear path, thereis a linear distance between any point in the tooth when determined atany two times during the treatment. Thus, an arbitrary point P1 may infact undergo a true side-to-side translation as indicated by arrow d1,while a second arbitration point P2 may travel along an arcuate path,resulting in a final translation d2. Many aspects of the presentinvention are defined in terms of the maximum permissible movement of apoint P1 induced on any particular tooth. Such maximum tooth movement,in turn, is defined as the maximum linear translation of that point P1on the tooth which undergoes the maximum movement for that tooth in anytreatment step.

FIG. 2C shows one adjustment appliance 111 which is worn by the patientin order to achieve an incremental repositioning of individual teeth inthe jaw as described generally above. The appliance is a polymeric shellhaving a teeth receiving cavity. This is described in U.S. applicationSer. No. 09/169,276, filed Oct. 8, 1998, which claims priority from U.S.Pat. No. 5,975,893, which in turn claims priority from provisionalapplication No. 60/050,352, filed Jun. 20, 1997 (collectively the “priorapplications”), the full disclosures of which are incorporated byreference.

As set forth in the prior applications, each polymeric shell may beconfigured so that its tooth receiving cavity has a geometrycorresponding to an intermediate or final tooth arrangement intended forthe appliance. The patient's teeth are repositioned from their initialtooth arrangement to a final tooth arrangement by placing a series ofincremental position adjustment appliances over the patient's teeth. Theadjustment appliances are generated at the beginning of the treatment,and the patient wears each appliance until the pressure of eachappliance on the teeth can no longer be felt. At that point, the patientreplaces the current adjustment appliance with the next adjustmentappliance in the series until no more appliance remains. Conveniently,the appliances are generally not affixed to the teeth and the patientmay place and replace the appliances at any time during the procedure.The final appliance or several appliances in the series may have ageometry or geometries selected to overcorrect the tooth arrangement,i.e., have a geometry which would (if fully achieved) move individualteeth beyond the tooth arrangement which has been selected as the“final.” Such overcorrection may be desirable in order to offsetpotential relapse after the repositioning method has been terminated,i.e., to permit some movement of individual teeth back toward theirprecorrected positions. Overcorrection may also be beneficial to speedthe rate of correction, i.e., by having an appliance with a geometrythat is positioned beyond a desired intermediate or final position, theindividual teeth will be shifted toward the position at a greater rate.In such cases, the use of an appliance can be terminated before theteeth reach the positions defined by the appliance.

The polymeric shell 111 can fit over all teeth present in the upper orlower jaw. Often, only certain one(s) of the teeth will be repositionedwhile others of the teeth will provide a base or an anchor region forholding the appliance 111 in place as the appliance 111 applies aresilient repositioning force against the tooth or teeth to berepositioned. In complex cases, however, multiple teeth may berepositioned at some point during the treatment. In such cases, theteeth which are moved can also serve as a base or anchor region forholding the repositioning appliance.

The polymeric appliance 111 of FIG. 2C may be formed from a thin sheetof a suitable elastomeric polymer, such as Tru-Tain 0.03 in, thermalforming dental material, available from Tru-Tain Plastics, Rochester,Minn. Usually, no wires or other means will be provided for holding theappliance in place over the teeth. In some cases, however, it will bedesirable or necessary to provide individual anchors on teeth withcorresponding receptacles or apertures in the appliance 111 so that theappliance can apply an upward force on the tooth which would not bepossible in the absence of such an anchor.

FIG. 3 shows a process 200 for producing the incremental positionadjustment appliances for subsequent use by a patient to reposition thepatient's teeth. As a first step, an initial digital data set (IDDS)representing an initial tooth arrangement is obtained (step 202). TheIDDS may be obtained in a variety of ways. For example, the patient'steeth may be scanned or imaged using X-rays, three dimensional X-rays,computer-aided tomographic images or data sets, or magnetic resonanceimages, among others. The teeth data may be generated by a destructivescanner, as described in the incorporated-by-reference U.S. applicationSer. No. 09/169,276, filed Oct. 8, 1998.

The IDDS is then manipulated using a computer having a suitablegraphical user interface (GUI) and software appropriate for viewing andmodifying the images. More specific aspects of this process will bedescribed in detail below.

Individual tooth and other components may be segmented or isolated inthe model to permit their individual repositioning or removal from thedigital model. After segmenting or isolating the components, the userwill often reposition the tooth in the model by following a prescriptionor other written specification provided by the treating professional.Alternatively, the user may reposition one or more teeth based on avisual appearance or based on rules and algorithms programmed into thecomputer. Once the user is satisfied, the final teeth arrangement isincorporated into a final digital data set (FDDS) (step 204). The FDDSis used to generate appliances that move the teeth in a specifiedsequence. First, the centers of each tooth model may be aligned using anumber of methods. One method is a standard arch. Then, the teeth modelsare rotated until their roots are in the proper vertical position. Next,the teeth models are rotated around their vertical axis into the properorientation. The teeth models are then observed from the side, andtranslated vertically into their proper vertical position. Finally, thetwo arches are placed together, and the teeth models moved slightly toensure that the upper and lower arches properly mesh together. Themeshing of the upper and lower arches together is visualized using acollision detection process to highlight the contacting points of theteeth.

Based on both the IDDS and the FDDS, a plurality of intermediate digitaldata sets (INTDDSs) are defined to correspond to incrementally adjustedappliances (step 206). Finally, a set of incremental position adjustmentappliances are produced based on the INTDDs and the FDDS (step 208).

In step 204, final positions for the upper and lower teeth in amasticatory system of a patient are determined by generating a computerrepresentation of the masticatory system. An occlusion of the upper andlower teeth is computed from the computer representation; and afunctional occlusion is computed based on interactions in the computerrepresentation of the masticatory system. The occlusion may bedetermined by generating a set of ideal models of the teeth. Each idealmodel in the set of ideal models is an abstract model of idealized teethplacement which is customized to the patient's teeth, as discussedbelow. After applying the ideal model to the computer representation,and the position of the teeth is optimized to fit the ideal model. Theideal model may be specified by one or more arch forms, or may bespecified using various features associated with the teeth.

FIG. 4 illustrates a process 300 which optimizes the final placement ofthe teeth based on teeth features. First, the process 300 automaticallyor, with human assistance, identifies various features associated witheach tooth to arrive at a model of the teeth (step 302). An ideal modelset of teeth is then generated either from casts of the patient's teethor from patients with a good occlusion (step 303).

From step 302, the process 300 positions the model of the teeth in itsapproximate final position based on a correspondence of features to theideal model (step 304). In that step, each tooth model is moved so thatits features are aligned to the features of a corresponding tooth in theideal model. The features may be based on cusps, fossae, ridges,distance-based metrics, or shape-based metrics. Shape-based metrics maybe expressed as a function of the patient's arches, among others.

For example, cusp features associated with each tooth may be used. Cuspsare pointed projections on the chewing surface of a tooth. In adetection stage, a possible cusp is viewed as an “island” on the surfaceof the tooth, with the candidate cusp at the highest point on theisland. “Highest” is measured with respect to the coordinate system ofthe model, but could just as easily be measured with respect to thelocal coordinate system of each tooth. The set of all possible cusps isdetermined by looking for all local maxima on the tooth model that arewithin a specified distance of the top of the bounding box of the model.First, the highest point on the model is designated as the firstcandidate cusp. A plane is passed through this point, perpendicular tothe direction along which the height of a point is measured. The planeis then lowered by a small predetermined distance along the Z axis.Next, all vertices connected to the tooth and which are above the planeand on some connected component are associated with the candidate cuspas cusps. This step is also referred to as a flood fill step. From eachcandidate cusp point, outward flooding is performed, marking each vertexon the model visited in this matter as part of the correspondingcandidate cusp. After the flood fill step is complete, every vertex onthe model is examined. Any vertex that is above the plane and has notbeen visited by one of the flood fills is added to the list of candidatecusps. These steps are repeated until the plane has traveled a specifieddistance.

After the detection stage, the cusp detection process may include arejection stage where local geometries around each of cusp candidatesare analyzed to determine if they possess non-cusp-like features. Cuspcandidates that exhibit non-cusp-like features are removed from the listof cusp candidates. Various criteria may be used to identifynon-cusp-like features. According to one test, the local curvature ofthe surface around the cusp candidate is used to determine whether thecandidate possesses non-cusp-like features. Alternatively, a measure ofsmoothness is computed based on the average normal in an area around thecandidate cusp. If the average normal deviates from the normal at thecusp by more than a specified amount, the candidate cusp is rejected.

Next, the process 300 computes an orthodontic/occlusion index (step306). One index which may be used is the PAR (Peer Assessment Rating)index. In addition to PAR, other metrics such as shape-based metrics ordistance-based metrics may be used.

The PAR index identifies how far a tooth is from a good occlusion. Ascore is assigned to various occlusal traits which make up amalocclusion. The individual scores are summed to obtain an overalltotal, representing the degree a case deviates from normal alignment andocclusion. Normal occlusion and alignment is defined as all anatomicalcontact points being adjacent, with a good intercuspal mesh betweenupper and lower buccal teeth, and with nonexcessive overjet andoverbite.

In PAR, a score of zero would indicate good alignment, and higher scoreswould indicate increased levels of irregularity. The overall score isrecorded on pre- and posttreatment dental casts. The difference betweenthese scores represents the degree of improvement as a result oforthodontic intervention and active treatment. The eleven components ofthe PAR Index are: upper right segment; upper anterior segment; upperleft segment; lower right segment; lower anterior segment; lower leftsegment; right buccal occlusion; overjet; overbite; centerline; and leftbuccal occlusion. In addition to the PAR index, other indices may bebased on distances of the features on the tooth from their idealpositions or ideal shapes.

From step 306, the process 300 determines whether additionalindex-reducing movements are possible (step 308). Here, all possiblemovements are attempted, including small movements along each major axisas well as small movements with minor rotations. An index value iscomputed after each small movement and the movement with the best resultis selected. In this context, the best result is the result thatminimizes one or more metrics such as PAR-based metrics, shape-basedmetrics or distance-based metrics. The optimization may use a number oftechniques, including simulated annealing technique, hill climbingtechnique, best-first technique, Powell method, and heuristicstechnique, among others. Simulated annealing techniques may be usedwhere the index is temporarily increased so that another path in thesearch space with a lower minimum may be found. However, by startingwith the teeth in an almost ideal position, any decrease in the indexshould converge to the best result.

In step 308, if the index can be optimized by moving the tooth,incremental index-reducing movement inputs are added (step 310) and theprocess loops back to step 306 to continue computing theorthodontic/occlusion index. Alternatively, in the event that the indexcannot be optimized any more, the process 300 exits (step 312).

Turning now to FIG. 5, a process 320 for performing functional occlusionis shown. Functional occlusion is a process for determining how well theteeth fit together when the jaws move. The process 320 first acquirestooth/arch jaw registration. This may be done using conventionaltechniques such as X-ray, a computer tomography, or a mechanical devicesuch as a face bow transfer (322).

After acquiring the registration information, the process 320 placesdigital dental models of the teeth in a digital articulation simulator(step 324). The articulation simulator allows a subset of jaw movementssuch as bite-movements to be simulated, as described below.

From step 324, the process 320 simulates jaw motions (step 326). Asimplified set of movement physics (kinematics) is applied to the dentalmodels. The process 320 performs a simulation using a simplified set ofinteracting forces on the jaws 100 and 101 in relation to one another.The simplified physical simulation allows the system to focus on motionsinvolving much contact between the jaws. The physical simulation allowsthe system to render realistic physically correct jaw movements when thejaws 100 and 101 come into contact with each other.

A range of simulated motion may be supplied using a library of motions.One typical motion supplied by the library is a protrusive motion wherethe lower jaw 101 is moved forward and backward to bring the front teethon both jaws into contact with each other. Another motion is a lateralmotion found in food chewing. The lateral motion involves moving thejaws 100 and 101 side to side. Other motions that may be supplied in thelibrary include motions that are “tooth guided” where the path of thelower jaw 100 is guided by the teeth in contact with each other.

Next, the process 320 adjusts the final position based on contactsobserved during the simulation of motions in step 326 (step 328). Theresult of the simulation is analyzed, the position of each tooth can beadjusted if contacts associated with that tooth are deemed excessive.

Finally, based on the contact data generated, the process determineswhether additional motion simulations need to be done. The motionsimulation may be rerun until the contacts associated with each toothare acceptable to the treating orthodontist. The tooth modelmanipulation process can be done subjectively, i.e., the user may simplyreposition teeth in an aesthetically and/or therapeutically desiredmanner based on observations of the final position or based on thesimulation of contacts. Alternatively, rules and algorithms may be usedto assist the user in repositioning the teeth based on the contacts. Ifthe simulation needs to be repeated, the process loops back to step 326(step 330). Alternatively, the process exits (step 332).

FIG. 6 shows an optional process of 340 of incorporating midtreatmentinformation to the final positioning process. First, a digital modelincorporating dental information associated with the patient isgenerated from a scan of the patient's teeth (step 342). The scan may beperformed using casts, X-rays or any of the conventional scanningmethods.

Next, the digital model is segmented into one model for each tooth (step344). Each tooth is then matched against a model associated with a priorscan developed at the beginning of the treatment plan (step 346). Thematching process is based on matching corresponding points between thecurrent scan and the prior scan of the teeth. In most cases, the teethsegmented from the current scan retain the shapes determined at thebeginning of the treatment plan, and the matching process is easybecause the models should be similar to each other.

A final position transform is then applied to the new teeth model (step348). The final position and specification from the prior model iscopied to the current model of the patient, and the final position isadjusted based on the new models, the new X-ray information or a newprescription (step 350). Step 350 basically involves rerunning theminimization process 300 (FIG. 4) described previously with the newinformation, which may be a slight change in the model, a change in theX-ray scan, or a change the prescription. Finally, the process 340 exits(step 352).

FIG. 7 is a simplified block diagram of a data processing system 500.Data processing system 500 typically includes at least one processor 502which communicates with a number of peripheral devices over bussubsystem 504. These peripheral devices typically include a storagesubsystem 506 (memory subsystem 508 and file storage subsystem 514), aset of user interface input and output devices 518, and an interface tooutside networks 516, including the public switched telephone network.This interface is shown schematically as “Modems and Network Interface”block 516, and is coupled to corresponding interface devices in otherdata processing systems over communication network interface 524. Dataprocessing system 500 may include a terminal or a low-end personalcomputer or a high-end personal computer, workstation or mainframe.

The user interface input devices typically include a keyboard and mayfurther include a pointing device and a scanner. The pointing device maybe an indirect pointing device such as a mouse, trackball, touchpad, orgraphics tablet, or a direct pointing device such as a touchscreenincorporated into the display. Other types of user interface inputdevices, such as voice recognition systems, may be used.

User interface output devices may include a printer and a displaysubsystem, which includes a display controller and a display devicecoupled to the controller. The display device may be a cathode ray tube(CRT), a flat-panel device such as a liquid crystal display (LCD), or aprojection device. The display subsystem may also provide nonvisualdisplay such as audio output.

Storage subsystem 506 maintains the basic programming and dataconstructs that provide the functionality of the present invention. Thesoftware modules discussed above are typically stored in storagesubsystem 506. Storage subsystem 506 typically comprises memorysubsystem 508 and file storage subsystem 514.

Memory subsystem 508 typically includes a number of memories including amain random access memory (RAM) 510 for storage of instructions and dataduring program execution and a read only memory (ROM) 512 in which fixedinstructions are stored. In the case of Macintosh-compatible personalcomputers the ROM would include portions of the operating system; in thecase of IBM-compatible personal computers, this would include the BIOS(basic input/output system).

File storage subsystem 514 provides persistent (nonvolatile) storage forprogram and data files, and typically includes at least one hard diskdrive and at least one floppy disk drive (with associated removablemedia). There may also be other devices such as a CD-ROM drive andoptical drives (all with their associated removable media).Additionally, the system may include drives of the type with removablemedia cartridges. The removable media cartridges may, for example behard disk cartridges, such as those marketed by Syquest and others, andflexible disk cartridges, such as those marketed by Iomega. One or moreof the drives may be located at a remote location, such as in a serveron a local area network or at a site on the Internet's World Wide Web.

In this context, the term “bus subsystem” is used generically so as toinclude any mechanism for letting the various components and subsystemscommunicate with each other as intended. With the exception of the inputdevices and the display, the other components need not be at the samephysical location. Thus, for example, portions of the file storagesystem could be connected over various local-area or wide-area networkmedia, including telephone lines. Similarly, the input devices anddisplay need not be at the same location as the processor, although itis anticipated that the present invention will most often be implementedin the context of PCS and workstations.

Bus subsystem 504 is shown schematically as a single bus, but a typicalsystem has a number of buses such as a local bus and one or moreexpansion buses (e.g., ADB, SCSI, ISA, EISA, MCA, NuBus, or PCI), aswell as serial and parallel ports. Network connections are usuallyestablished through a device such as a network adapter on one of theseexpansion buses or a modem on a serial port. The client computer may bea desktop system or a portable system.

Scanner 520 is responsible for scanning casts of the patient's teethobtained either from the patient or from an orthodontist and providingthe scanned digital data set information to data processing system 500for further processing. In a distributed environment, scanner 520 may belocated at a remote location and communicate scanned digital data setinformation to data processing system 500 over network interface 524.

Fabrication machine 522 fabricates dental appliances based onintermediate and final data set information received from dataprocessing system 500. In a distributed environment, fabrication machine522 may be located at a remote location and receive data set informationfrom data processing system 500 over network interface 524.

Various alternatives, modifications, and equivalents may be used in lieuof the above components. Although the final position of the teeth may bedetermined using computer-aided techniques, a user may move the teethinto their final positions by independently manipulating one or moreteeth while satisfying the constraints of the prescription.

Additionally, the techniques described here may be implemented inhardware or software, or a combination of the two. The techniques may beimplemented in computer programs executing on programmable computersthat each includes a processor, a storage medium readable by theprocessor (including volatile and nonvolatile memory and/or storageelements), and suitable input and output devices. Program code isapplied to data entered using an input device to perform the functionsdescribed and to generate output information. The output information isapplied to one or more output devices.

Each program can be implemented in a high level procedural orobject-oriented programming language to operate in conjunction with acomputer system. However, the programs can be implemented in assembly ormachine language, if desired. In any case, the language may be acompiled or interpreted language.

Each such computer program can be stored on a storage medium or device(e.g., CD-ROM, hard disk or magnetic diskette) that is readable by ageneral or special purpose programmable computer for configuring andoperating the computer when the storage medium or device is read by thecomputer to perform the procedures described. The system also may beimplemented as a computer-readable storage medium, configured with acomputer program, where the storage medium so configured causes acomputer to operate in a specific and predefined manner.

FIG. 8 shows an exemplary process for fitting the ideal teeth. First,the process provides a static occlusion determined from a computerrepresentation of the masticatory system. Next, the process models anideal set of teeth and automatically applies the ideal set of teeth tothe computer representation of the masticatory system of the patient.Further, the process optimizes the position of the patient's teeth tofit the ideal set of teeth.

Further, while the invention has been shown and described with referenceto an embodiment thereof, those skilled in the art will understand thatthe above and other changes in form and detail may be made withoutdeparting from the spirit and scope of the following claims.

What is claimed is:
 1. A method of generating shell appliancesconfigured to resiliently reposition a patient's teeth, the methodcomprising: receiving a first digital data set representing a firstarrangement of the patient's teeth; generating a final position digitaldata set representing the patient's teeth in a desired or prescribedfinal arrangement; generating a plurality of intermediate digital datasets representing different intermediate arrangements of the patient'steeth, wherein at least some of the intermediate tooth arrangementsrepresent different orthodontic treatment stages as the patient's teethare moved from the first arrangement toward the final arrangement; andafter generating the plurality of intermediate digital data sets,generating a plurality of shell appliances based on the plurality ofintermediate digital data sets, the plurality of shell appliances eachhaving cavities shaped to receive and resiliently reposition teeth alongrespective movement paths for the teeth between the first arrangementand the final arrangement.
 2. The method of claim 1, comprising:receiving an mid-treatment position digital data set representing amid-treatment arrangement of the patient's teeth, the mid-treatmentposition digital data set defining mid-treatment shapes for thepatient's teeth; generating a mid-treatment approximate final positiondigital data set by modifying the mid-treatment position digital dataset to reposition representations of the patient's teeth based on thepositions of corresponding teeth in the final position digital data set;generating a mid-treatment final position digital data set representinga mid-treatment final arrangement of the patient's teeth by modifyingthe mid-treatment approximate final position digital data set based onan analysis of contact between upper and lower teeth having themid-treatment shapes so as to improve an occlusion; and generating aplurality of mid-treatment intermediate digital data sets representingmid-treatment intermediate arrangements of the patient's teeth, whereinat least some of the mid-treatment intermediate tooth arrangementsrepresent different orthodontic treatment stages as the patient's teethare moved from the mid-treatment arrangement toward the mid-treatmentfinal arrangement.
 3. The method of claim 2, wherein said analysis ofcontact comprises: generating a mid-treatment computer representation ofa masticatory system of the patient that includes upper and lower teethas defined by the mid-treatment approximate final position data set;using the mid-treatment computer representation of the masticatorysystem to simulate motion of the masticatory system to generate contactdata indicative of contacts between the upper and lower teeth; andplacing a tooth in a mid-treatment final position based on the contactdata.
 4. The method of claim 3, wherein said placing a tooth in amid-treatment final position is based on a measure of undesirability ofthe contacts.
 5. The method of claim 4, wherein said generating amid-treatment final position digital data set comprises optimizing theposition of the tooth to minimize the measure of undesirability.
 6. Themethod of claim 1, wherein at least two of the shell appliances havedifferent cavity geometries.
 7. The method of claim 1, wherein the firstarrangement represents an intermediate arrangement of the patient'steeth between an initial measured arrangement and the final arrangement.8. The method of claim 7, wherein said generating a plurality of shellappliances comprises controlling a fabrication machine to fabricate apatient removable appliance for each of at least two of the intermediatearrangements.
 9. The method of claim 1, wherein said generating a finalposition digital data set comprises: arranging representations of thepatient's teeth based on an ideal model.
 10. The method of claim 9,wherein said generating a final position digital data set comprisesdetermining an arch form based on the patient's teeth.
 11. The method ofclaim 9, wherein the ideal model is customized based on the patient'steeth.
 12. The method of claim 9, wherein said patient has a masticatorysystem and said generating a final position digital data set comprisesrepositioning one or more of representations of teeth to improve anocclusion between upper and lower teeth of the patient.
 13. The methodof claim 12, wherein said generating a final position digital data setcomprises: generating a computer representation of a masticatory systemof the patient that includes upper and lower teeth; using the computerrepresentation of the masticatory system to simulate motion of themasticatory system to generate contact data indicative of contactsbetween the upper and lower teeth; and placing a tooth in a finalposition based on the contact data.
 14. The method of claim 13, whereinsaid placing step is based on a measure of undesirability of thecontacts.
 15. The method of claim 14, wherein said generating a finalposition digital data set comprises optimizing the position of the toothto minimize the measure of undesirability.
 16. The method of claim 15,wherein the measure of undesirability is a function of one or more ofPeer Assessment Rating (PAR) metrics, distance-based metrics, orshape-based metrics.
 17. A method of generating shell appliancesconfigured to resiliently reposition a patient's teeth, the methodcomprising: receiving a first digital data set representing a firstarrangement of the patient's teeth; segmenting the first digital dataset into a plurality of manipulable tooth components; generating aplurality of intermediate digital data sets based on the plurality ofmanipulable tooth components, the plurality of intermediate digital datasets representing different intermediate arrangements of the patient'steeth, wherein at least some of the intermediate tooth arrangementsrepresent different orthodontic treatment stages as the patient's teethare moved from the first arrangement toward a final arrangement; andgenerating a plurality of shell appliances based on the plurality ofintermediate digital data sets after generating the plurality ofintermediate digital data sets, the plurality of shell appliances eachhaving cavities shaped to receive and resiliently reposition teeth alongrespective movement paths for the teeth between the first arrangementand the final arrangement.
 18. The method of claim 17, wherein the firstarrangement represents an intermediate arrangement of the patient'steeth between an initial measured arrangement and the final arrangement.19. The method of claim 17, further comprising repositioning one or moreof the plurality of manipulable tooth components to improve an occlusionbetween upper and lower teeth of the patient.
 20. The method of claim17, further comprising: generating a computer representation of amasticatory system of the patient that includes upper and lower teeth;using the computer representation of the masticatory system to simulatemotion of the masticatory system to generate contact data indicative ofcontacts between the upper and lower teeth; and placing a tooth in afinal position based on the contact data.
 21. The method of claim 20,wherein said placing step is based on a measure of undesirability of thecontacts.
 22. The method of claim 21, further comprising optimizing theposition of the tooth to minimize the measure of undesirability.
 23. Themethod of claim 22, wherein the measure of undesirability is a functionof one or more of Peer Assessment Rating (PAR) metrics, distance-basedmetrics, or shape-based metrics.
 24. The method of claim 17, whereinsaid generating a plurality of shell appliances comprises controlling afabrication machine to fabricate a patient removable appliance for eachof at least two of the intermediate arrangements.
 25. A method ofgenerating shell appliances configured to resiliently reposition apatient's teeth, the method comprising: receiving a first digital dataset representing a first arrangement of the patient's teeth;manipulating a plurality of segmented tooth components based on thefirst digital data set so as to generate a plurality of intermediatedigital data sets representing intermediate arrangements of thepatient's teeth, wherein at least some of the intermediate tootharrangements represent different orthodontic treatment stages as thepatient's teeth are moved from the first arrangement toward a finalarrangement; and after generating the plurality of intermediate digitaldata sets, generating a plurality of shell appliances based on theplurality of intermediate digital data sets, the plurality of shellappliances each having cavities shaped to receive and resilientlyreposition teeth along respective movement paths for the teeth betweenthe first arrangement and the final arrangement.
 26. The method of claim25, wherein the first arrangement represents an intermediate arrangementof the patient's teeth between an initial measured arrangement and thefinal arrangement.
 27. The method of claim 25, further comprisingrepositioning one or more of the plurality of segmented tooth componentsto improve an occlusion between upper and lower teeth of the patient.28. The method of claim 25, further comprising: generating a computerrepresentation of a masticatory system of the patient that includesupper and lower teeth; using the computer representation of themasticatory system to simulate motion of the masticatory system togenerate contact data indicative of contacts between the upper and lowerteeth; and placing a tooth in a final position based on the contactdata.
 29. The method of claim 28, wherein said placing step is based ona measure of undesirability of the contacts.
 30. The method of claim 29,further comprising optimizing the position of the tooth to minimize themeasure of undesirability.
 31. The method of claim 30, wherein themeasure of undesirability is a function of one or more of PeerAssessment Rating (PAR) metrics, distance-based metrics, or shape-basedmetrics.
 32. The method of claim 25, wherein said generating a pluralityof shell appliances comprises controlling a fabrication machine tofabricate a patient removable appliance for each of at least two of theintermediate arrangements.